1. Field of the Invention
This invention relates generally to powders for use in thermal barrier coatings and high-temperature abradable coatings, and more particularly to high-purity fused and crushed zirconia alloy powder for use with thermal spray deposition processes.
2. Description of Related Art
Superior high-temperature properties are required to improve the performance of heat resistant and corrosion resistant members. These members include, for example, gas turbine blades, combustor cans, ducting and nozzle guide vanes in combustion turbines and combined cycle power plants. Turbine blades, for example, are driven by hot gasses, and the efficiency of the gas turbine increases with the rise in operation temperature. The demand for continued improvement in efficiency has driven the system designers to specify increasingly higher turbine inlet temperatures. Thus, there is a continuing need for materials that can achieve higher operational temperatures.
Ceramic coatings generally have been used to allow standard materials to operate in higher temperature environments. Ceramic thermal barrier coatings and high temperature abradable coatings may be applied using, for example, a thermal spray process. In one form of this process, ceramic powder feedstock is injected into a high velocity plasma stream where it is simultaneously melted and propelled toward a substrate.
One factor that impacts coating lifetime is the sintering rate of the coating. When the coating is cycled above half of its absolute melting temperature, the coating begins to sinter causing volume shrinkage. As the coating shrinks, the stress difference between the coating and substrate increases. At a certain amount of shrinkage (which varies depending on the type of structure), the stress difference exceeds the adhesive or cohesive strength of the coating and it becomes detached. Decreasing the sintering rate increases the amount of time before the critical shrinkage is achieved, so it can become a major design consideration.
As industry demands continue to drive higher operating temperatures, there remains a need in the art for coating materials that can meet performance requirements at increasingly higher temperatures.